This invention is in the field of wheelchair lifts for lifting and lowering wheelchairs between the floor level of a commercial vehicle and street level. Among other problems in designing such mechanisms is to provide a compact structure which will not impede normal ingress or egress to and from the vehicle but can be easily and rapidly moved into position across a doorway and, under the complete control of the vehicle operator, move the wheelchair and its occupant onto and from the vehicle in a minimum amount of time. In this connection, it is desirable that the system be so constructed and arranged as to strap in the wheelchair on the lift when being lifted or lowered together with adequate siderails and the removal of hinges along any intermediate sections of the platform for smooth entry and exit.
Representative U.S. Patents in this field are U.S. Pat. Nos. 4,479,753 to G. R. Thorley, 4,534,450 to P. Savaria, 4,299,528 to J. E. Kazeil et al and 4,140,230 to M. R. Pearson. In addition to the foregoing, there is commercially available a wheelchair lift mechanism manufactured and sold by Gustaf Bruns Gmbh & Co. of the Federal Republic of Western Germany under the trademark "AMF HUBMATIK" BSL 350 and which is of a type designed for use in commercial vehicles having a foldable platform assembly mounted on a rotation column for swinging movement between a stored position alongside a doorway into the vehicle to an extended position across the doorway for the purpose of lifting and lowering a wheelchair and its occupant between the floor level of the vehicle and street level.
Among other problems associated with the "AMF HUBMATIK" BSL 350 design is the lack of a stable column for the platform sections, smooth and reliable operation of the platform sections and secure latching either in a raised or stored position a lowered or operative position; and further the lack of control over the platform as it is raised and lowered and the tendency of the telescoping mount to bind in lifting and lowering the platform. Another problem overcome by the present invention is a system which can be retrofit to existing buses and in such a way as to readily conform to different height requirements between the floor level and street level without sacrificing any stability or reliability in the system.
Considering other desirable features of a wheelchair lift, it is important to provide for a rotation column capable of supporting a telescoping platform assembly for movement into and out of an operative position, and an improved lock-type attachment for the platform assembly for locking in the operative and inoperative stored position. Moreover, it is desirable that the platform assembly be securely retained in the stored position and which, once released, requires that a positive pressure be applied in lowering the platform into an operative position.